Solution mining of salt and storage of industrial fluids

ABSTRACT

A system for solution mining a salt deposit and simultaneously storing an industrial fluid, while conserving system heat input and minimizing earth surface polluting impurity extractions from an underground salt deposit. The invention provides an improved method for conserving system input heat, and utilizing it to improve a solution mining operation in an underground salt mineral deposit; whereby to produce a purified brine at reduced cost. The majority of the mineral deposit impurities are left underground, thereby reducing the recovery plant earth surface polluting effluent problem. Incidentally, the system provides an improved underground storage system for industrial fluid commodities such as liquid chlorine; carbon tetrachloride; carbon bisulfide, and the like.

United States Patent [191 [111 3,724,898 Jacoby [451 Apr. 3, 1973 [54]SOLUTION MINING OF SALT AND STORAGE OF INDUSTRIAL FLUIDS H07 BR/Nf l,PRODUCT Primary Examiner-Ernest R. Purser Attorney-Bean & Bean [57]ABSTRACT A system for solution mining a salt deposit and simultaneouslystoring an industrial fluid, while conserving system heat input andminimizing earth surface polluting impurity extractions from anunderground salt deposit. The invention provides an improved method forconserving system input heat, and utilizing it to improve a solutionmining operation in an underground salt mineral deposit; whereby toproduce a purified brine at reduced cost. The majority of the mineraldeposit impurities are left underground, thereby reducing the recoveryplant earth surface polluting effluent problem. lncidentally, the systemprovides an improved underground storage system for industrial fluidcommodities such as liquid chlorine; carbon tetrachloride; carbonbisulfide, and the like.

12 Claims, 1 Drawing Figure PATENTED APR 3 I975 l2 LL/0 U/Q CHL OQ/NEHOT BR/A/f PRODUCT AIR may

SALT E :IZLji HOT WATER CENTRAL/ZEPS I I I I i glm fm lm fim ROCK LA YERCHARLES H. JACOBY I A TTOANE Y5 SOLUTION MINING OF SALT AND STORAGE OFINDUSTRIAL FLUIDS BACKGROUND AND OBJECTS OF THE INVENTION This inventionrelates to the mining of soluble minerals and concomitant storage offluid commodities; and more particularly to the mining of sodiumchloride or other such soluble mineral salt deposits includingimpurities; the absolute and relative solubilities of which vary withtemperature and/or pressure changes. More specifically, the inventionrelates to an improved process for simultaneously beneficiating andmining salt from a rock salt deposit, as discussed for example incommonly assigned US. Pat. Nos. 2,555,340; 2,876,182 and 3,348,883.

As explained in the aforesaid patents, sources of salt such as minedrock salt, usually consists of sodium chloride to the extent of about 90to 99 percent; the balance being impurities such as sulphates,silicates, carbonates, etc.; calcium sulphate being the principalimpurity. According to typical prior refining procedures, such impuresalts have been refined" in some instances by treatment of salinesolutions obtained directly from wells, or from water-solutions producedby dissolving previously mined impure rock salt substances in water orother suitable solvents, by the use of vacuum-evaporator systems.

Uniquely encountered in the art of solution-mining underground rock saltdeposits is the fact that rock salt in situ is an exceptionally highrate heat conductive medium compared to the other geological formationsenvironmental thereto. In consequence, a typical rock salt solutionmining operation in a horizontally disposed rock salt deposit employingheated water as the mining solvent is inherently beset with huge andexpensive operational heat input losses, due to the rapid dissipation ofheat from the solvent solution through the relatively broad surfaceareas of the floor and ceiling of the solution cavity. Such heat lossestypically account for enormous operating heat supply requirements, suchas may render an operation marginally profitable or unprofitable; and itis specifically an ob ject of the present invention to provide animproved operative system and technique for such purposes; whereby torealize substantial product improvement and plant completion investmentand operating economies.

Another object is to provide an improved system as aforesaid whereby tobetter conserve the heat involved in a solution mining operation, whileusefully and simultaneously storing a liquid or gas commodity.

Other objects and advantages of the present invention will be apparentfrom the following specification and the accompanying drawing wherein:

THE DRAWING The FIGURE illustrates diagrammatically by way of a verticalsectional view, a geological formation including a typical salt bed inprocess of being mined in accordance with the present invention.

As discussed in detail by way of example herein, the invention isembodied in a system for simultaneously mining a purified sodiumchloride salt product from an underground deposit of relatively impurerock salt or the like, while simultaneously storing a reserve supply ofliquid chlorine. Further, by way of example the invention is illustratedas being employed in conjunction with a solution mining system wherein areserve supply of liquid chlorine is disposed to cover the bottom of thesolution cavity while a heat insulating pneumatic pad of air (ornitrogen, Freon, krypton, xenon, neon, argon, benzine or other lighthydrocarbons, or the like) is maintained on top of the solventcirculating within the cavity, so as to heat-insulate the solvent fromthe roof of the cavity. However, it is to be understood that theinvention may be usefully applied to the mining of other forms ofsoluble mineral deposits, such as sodium borate, potash, and the like;and to the storage of liquid commodities other than chlorine, such ascarbon tetrachloride, carbon bisulphide, or the like.

In any case, inasmuch as the mining solvent preferably comprises wateror dilute brine which is heated at the earth surface plant, the'pads ofair and chlorine or the like function as efficient heat insulatingdevices operating to conserve the heat of the solvent supply. Theinverse solubility characteristic of sodium chloride vs. calciumsulphate (a common impurity) is thus utilized to improved advantage tominimize dissolution of impurities into the product brine at the situsof the solution mining action. The cavity is maintained under sufficientpressure so as to keep the chlorine or other commodity in liquid state;whereby the cavity also provides an ideal reserve chlorine supplystorage facility.

The solution mining cavity is illustrated by way of example in thedrawing herewith at 10, and is interconnected with the well head andsurface plant facility as illustrated diagrammatically at 12 by means ofa single well bore 14. The well bore is lined by means of an outercasing 16 inside of which progressively reduced diameter tubings18-20-22 are hung. The outer casing 16 is preferably anchored to thebore hole wall as by means of concrete or the like as indicated at 24.

The central tube 22 extends at its nether end beyond the lower level ofthe casing 20 and is fitted at its upper end with a supply conduit andcontrol valve arrangement as indicated at 26, whereby liquid chlorine orthe like (as explained hereinabove) may be pumped into the cavity underpressure so as to provide the liquid chlorine pad across the bottom ofthe solution cavity. The casing 18 terminates at its lower end at alevel somewhat higher than the lower end of the casing 20, and thus theannular space between the casings 18 and 20 provides the passageway forinlet of solvent (such as hot water or heated dilute brine). The solventis thereby circulated throughout the solution cavity to provide aconcentrated brine solution which then exits from the solution cavityupwardly through the annular space provided between the tubing 22 andthe casing 20.

Supply of solvent to the system is provided for at the surface plantfacility and is controlled by an inlet control valve unit as illustratedat 28; while the brine product exits from the casing 20 through means ofan outlet conduit and control valve arrangement as illustrated at 30.The outer casing 16 terminates at its lower end at an elevation somewhathigher than the bottom level of the casing 18, and thus the annularspace between the casings l6 and 18 provides a passageway for supply ofair (or other gaseous material) whereby to maintain the upper heatinsulating pad within the cavity above the body of solvent as itcirculates throughout the cavity in contact with the peripheral wallsthereof. Control of the supply and level of air or other gas in thecavity is maintained by means of an inlet conduit and control valve asshown at 32.

Thus, it will be appreciated that whereas the chlorine or similarcommodity is maintainable in the cavity under pressure pending itsrecovery and use, it functions in the meantime as a heat insulatingblanket between the floor of the cavity and the body of solvent andbrine as it circulates around the cavity walls; while the pneumatic padheat-insulates the brine from the roof of the cavity. The height of rocksalt wall or face exposed to the solvent is readily controlled byadjustments of the pneumatic and chlorine levels; and thus it will beunderstood that the mining operation may be readily controlled throughsimple adjustments of the valve devices at the surface plant facility.In this manner the rate of flow of materials through the system, as wellas the temperatures and pressures thereon, may be effectively monitoredto maintain the optimum processing conditions for full utilization ofthe inverse solubility phenomenon as explained hereinabove. Hence, aconsistently improved quality purified salt product is produced, whileunderground heat losses are reduced with substantial consequentoperating economies. Whereas the invention has been illustrated anddescribed in detail hereinabove in conjunction with a single well boresystem, it is to be understood that the invention is equally applicableto a multiple well bore system wherein one or more well bores operate as,injection wells, and one or more well bores operate as productionwells.

I claim:

1. A salt mine comprising,

a horizontally extended cavity in a salt deposit,

a blanket of a low heat conductivity liquid commodity-in-storagesubstantially covering the floor of the cavity,

a body of salt brine floating on top of the liquid commodity,

a blanket of fluid of low heat conductivity material floating on top ofthe brine and against the roof of the cavity, whereby the salt brinecontacts the cavity walls substantially only at the peripheral side wallportions thereof,

means for continuously removing brine from the cavity,

and means-for continuously adding salt solvent to the cavity at atemperature substantially higher than that of the salt depositsurrounding said cavity.

2. A salt mine according to claim 1 wherein the fluid of lowconductivity is air in gaseous form, and wherein means are provided forindependently and selectively supplying the liquid commodity and air inthe cavity and maintaining them under controlled pressures in thecavity.

3. A salt mine according to claim 2 wherein the liquid commodityischlorine and the means for supplying chlorine to the cavity isacentral pipe and concentric with it are annular passageways for flowinghot water to the cavity and brine away from the cavity.

4. A salt mine according to claim 3 wherein the cavity is maintainedunder sufficient pressure to keep the chlorine in liquid form andprevent appreciable boiling away thereof.

5. A method of mining salt from the sides of a cavity in a salt depositwithout removing salt from the top and bottom thereof which comprises,

adding to a cavity in a salt deposit in any suitable order chlorine andwater or brine, and a fluid of low conductivity which is lighter thanthe water or brine and chlorine whereby to fill the cavity with threelayers of fluids, comprising liquid chlorine at the bottom; brine at anintermediate level, and the lightweight fluid in the upper portion ofthe cavity; adding water or unsaturated brine to the cavity at atemperature substantially higher than that of the salt depositsurrounding said cavity and removing a brine of higher concentrationfrom the cavity, whereby the cavity is enlarged at the sides thereoffrom which the salt has been solution mined.

6. A method according to claim 5 wherein the cavity is substantiallyhorizontal, the fluid of low conductivity is air in gaseous form,pressure is maintained on the cavity to keep the chlorine in liquidform, water is added to the brine in the cavity, brine is removed fromthe cavity and the air and chlorine are maintained in their respectivepositions in the cavity.

7. A method according to claim 6 wherein water is added to the cavityand brine is removed therefrom through concentrically disposedcontiguous passageways, whereby heat losses to the walls surroundingsuch passageways are minimized.

8. A method according to claim 7 wherein the brine removal passageway isinside the hot water addition passageway thereby preventing cooling ofthe brine and avoiding crystallizing out of salt, and wherein the hotwater addition passageway is insulated from the surrounding wallmaterials by a layer of confined air.

9. The method of solution mining salt while simultaneously effectingstorage of at least one fluid, which comprises the steps of:

a. forming a solution mining cavity in an underground salt deposit;

b. forming a first heat insulating layer covering and in contact withthe floor area of said cavity and a second heat insulating layercovering and in contact with the roof area of said cavity andcontinuously introducing a liquid solvent for said salt into said cavitywhile simultaneously continuously withdrawing said solvent with the saltdissolved therein from said cavity, said first heat insulating layerconsisting of a storage liquid which is a nonsolvent for the salt and ismore dense than said solvent, said second heat insulating layerconsisting of a gas, and said solvent being introduced from a surfacefacility at a temperature substantially higher than that of said cavity;

. maintaining flow communication from a point within said first layer toa surface facility whereby to allow storage introduction and usewithdrawal of said storage liquid at will and independently of thesolution mining of said salt;

. maintaining flow communication from a point within said second layerand a surface facility whereby to allow introduction and withdrawal oftroduced and maintained at a pressure sufficient to maintain saidstorage liquid in liquid form while said second layer is maintained ingaseous form.

11. The method of solution mining and storage as defined in claim 10wherein said storage liquid is chlorine.

12. The method of solution mining and storage as defined in claim 11wherein said gas constituting the second layer is air.

2. A salt mine according to claim 1 wherein the fluid of lowconductivity is air in gaseous form, and wherein means are provided forindependently and selectively supplying the liquid commodity and air inthe cavity and maintaining them under controlled pressures in thecavity.
 3. A salt mine according to claim 2 wherein the liquid commodityis chlorine and the means for supplying chlorine to the cavity is acentral pipe and concentric with it are annular passageways for flowinghot water to the cavity and brine away from the cavity.
 4. A salt mineaccording to claim 3 wherein the cavity is maintained under sufficientpressure to keep the chlorine in liquid form and prevent appreciableboiling away thereof.
 5. A method of mining salt from the sides of acavity in a salt deposit without removing salt from the top and bottomthereof which comprises, adding to a cavity in a salt deposit in anysuitable order chlorine and water or brine, and a fluid of lowconductivity which is lighter than the water or brine and chlorinewhereby to fill the cavity with three layers of fluids, comprisingliquid chlorine at the bottom; brine at an intermediate level, and thelightweight fluid in the upper portion of the cavity; adding water orunsaturated brine to the cavity at a temperature substantially higherthan that of the salt deposit surrounding said cavity and removing abrine of higher concentration from the cavity, whereby the cavity isenlarged at the sides thereof from which the salt has been solutionmined.
 6. A method according to claim 5 wherein the cavity issubsTantially horizontal, the fluid of low conductivity is air ingaseous form, pressure is maintained on the cavity to keep the chlorinein liquid form, water is added to the brine in the cavity, brine isremoved from the cavity and the air and chlorine are maintained in theirrespective positions in the cavity.
 7. A method according to claim 6wherein water is added to the cavity and brine is removed therefromthrough concentrically disposed contiguous passageways, whereby heatlosses to the walls surrounding such passageways are minimized.
 8. Amethod according to claim 7 wherein the brine removal passageway isinside the hot water addition passageway thereby preventing cooling ofthe brine and avoiding crystallizing out of salt, and wherein the hotwater addition passageway is insulated from the surrounding wallmaterials by a layer of confined air.
 9. The method of solution miningsalt while simultaneously effecting storage of at least one fluid, whichcomprises the steps of: a. forming a solution mining cavity in anunderground salt deposit; b. forming a first heat insulating layercovering and in contact with the floor area of said cavity and a secondheat insulating layer covering and in contact with the roof area of saidcavity and continuously introducing a liquid solvent for said salt intosaid cavity while simultaneously continuously withdrawing said solventwith the salt dissolved therein from said cavity, said first heatinsulating layer consisting of a storage liquid which is a nonsolventfor the salt and is more dense than said solvent, said second heatinsulating layer consisting of a gas, and said solvent being introducedfrom a surface facility at a temperature substantially higher than thatof said cavity; c. maintaining flow communication from a point withinsaid first layer to a surface facility whereby to allow storageintroduction and use withdrawal of said storage liquid at will andindependently of the solution mining of said salt; d. maintaining flowcommunication from a point within said second layer and a surfacefacility whereby to allow introduction and withdrawal of said gas atwill and independently of the solution mining of said salt; and e.maintaining the introduction of said solvent at a point above said firstlayer and the withdrawal of solvent with dissolved salt at a pointbetween said first and second layers whereby to leave the first andsecond layers undisturbed by the solution mining operation.
 10. Themethod of solution mining and storage as defined in claim 9 wherein saidstorage liquid is a gas at atmospheric pressure and wherein said solventis introduced and maintained at a pressure sufficient to maintain saidstorage liquid in liquid form while said second layer is maintained ingaseous form.
 11. The method of solution mining and storage as definedin claim 10 wherein said storage liquid is chlorine.
 12. The method ofsolution mining and storage as defined in claim 11 wherein said gasconstituting the second layer is air.